Choosing a heat pump

1. How many kW?

The most important thing when choosing a heat pump is getting one that's the right size for the area/room you're heating. A model with insufficient heat output (kW) won’t keep your home at a desired temperature without working too hard and using too much power. However, an oversized unit costs more than you need to spend, and will reach the set temperature quickly so will be constantly turning on and off, which increases wear and tear.

For a guide, the table below shows approximate heat outputs required for a well-insulated living room with standard 2.4m ceilings. But it varies considerably depending on the area of windows and the number of external walls, among other factors.

For a more precise guide on how many kW you need, use our calculator. This is also a good way to check if a heat pump recommended by an installer is the right size for the job.

2. Heating/cooling efficiency

Look for models that are about the size calculated or 0.5kW more (so if you need 4.5kW, look for models between 4.5 and 5.0kW). Then, use our “Heating efficiency” scores and remove any heat pump with a below average (less than 7.0) score. If possible, only consider models scoring 8.0 or above. If you’re going to be using it as an air conditioner during summer, then also consider the cooling efficiency scores.

3. Low-temperature performance

The next step is considering the climate in your part of the country. The manufacturer’s claimed heat output and efficiency (COP) are based on tests conducted at 7°C, but below this temperature performance falls off dramatically. Our “low temperature score” is based on the performance at 2°C.

If you’re in an area where winter temperatures regularly drop below 5°C, choose a heat pump with a low temperature performance score above 7.0. This is important as heat pumps are most likely to frost up (where ice forms on the compressor coils) between 0°C and 5°C. They’ll then need to go into defrost mode for 20 minutes or more, which means they’ll be focussing energy on defrosting rather than heating.

4. High-wall or floor-mount?

Then, consider whether you want a high-wall or floor-mounted console. We think floor-mounts are the best bet for quick heating if you’ve got the floor space, but if you want a more out-of-sight heater then high-walls are also a good option. Ceiling cassettes, where the indoor unit is mounted into the ceiling, are worth considering if you lack wall or floor space.

5. Noise levels

Models with noise scores greater than 7.0 are quieter than average for their size. Consider the noise of both the indoor and outdoor unit, as a noisy outdoor unit can aggravate neighbours, while a loud indoor unit can make you pine for your old inefficient oil-column heater.

6. Extra features

You can whittle the choice down further by considering features such as:

• Most models come with a 24-hour timer, but some include a seven-day timer allowing you to set the heat pump differently on weekends.
• WiFi lets you control your heat pump with an app on your smart device. They’re more versatile and easier to use than a timer.
• There's no such thing as an attractive-looking heat pump, but some manufacturers offer models in multiple colours or slimline indoor units.
• Most heat pumps incorporate a washable filter unit that removes dust and particles from the air, important for people with asthma and allergies. These vary in quality and the types of particles they remove.
• Some high-end heat pumps feature motion sensors, which automatically turn the heat pump down when you leave the room, and a few models can even direct warm air away from you to reduce annoying draughts.
• Automatic de-icing is vital if you live in a cold area – otherwise, in winter, the pump will stop providing heat because of frost build-up on the outdoor heat-exchanger coils. This is a standard feature on newer inverter models.

7. Choose a good installer

You should get two or three installers to provide detailed quotes and proposed installation plans. When choosing an installer, ensure they follow EECA’s good practice guide to heat pump installation, are brand accredited for the heat pumps they install and have experience installing heat pumps in your area. They should be able to offer references for local jobs.

When you have the quotes, there are some checks you can do to give peace of mind that the proposed installation will get the best from out of the heat pump:

• The outdoor unit should be installed in an unobtrusive place on a north, west or east wall (so it gets some sun), not too close to neighbours where they could be upset by the noise or below bedroom windows, and somewhere where air can circulate freely around the unit.
• If the indoor and outdoor units are going to be greater than three or four metres away from each other, confirm with the heat pump installer that this won’t affect performance. Long pipe run lengths can reduce efficiency.
  
• If you live in a coastal area, or an area with high atmospheric sulphur (Rotorua for example), make sure you have been quoted for a corrosion-resistant outdoor unit. Once the job’s done, check the installers work. If it fails to satisfy the following checks, contact the installer and ask them to rectify it immediately:
• The indoor and outdoor units are well-secured with no likelihood of toppling over.
• The outdoor unit has at least 100mm (four inches) clearance from the ground.
• There’s no vibration or noise from the outdoor unit likely to disturb neighbours.
• The area around the unit is clear and the ducting and wiring is neat and tidy.
• The gaps where the ducting enters the home have been sealed.
• The water drainage hose discharges into an appropriate drain and not onto paths or under your home.

See our full guide to heat pump installation and costs for more info.

8. Use it wisely

Even if you’ve bought the perfect heat pump for your home, and your installer’s done everything by the book, you won’t get the most out of it if you don’t use it properly:

• Only leave your heat pump on all day, every day, if your home is well-sealed and has comprehensive insulation. In draughty villas, you’re better off only switching it on when required.
• Don’t set the controller to a higher temperature than required. Selecting 30°C in an effort to warm a room extra fast doesn’t work – set the temperature you want (we recommend 21-23°C) and let the heat pump do the rest.
• If your heat pump spends twenty minutes defrosting on cold winter mornings, use the timer to turn it on half an hour before you get up, or leave it on overnight at a low level if your home is well-sealed.
• Vacuum the filter on the indoor unit every three months. Regularly inspect the outdoor unit to ensure it hasn’t become overgrown or clogged with debris, while looking out for rust. Beware of cold callers pressuring you into expensive heat pump servicing. They often charge hundreds of dollars for a service you can perform yourself in a few minutes.